Hull resistance analysis Residual problem

sdkozm · September 30, 2013, 06:13

Hi friends...

I have a problem with my simulation. I try to calculate hull resistance, and the brief information about my simulation is that:

about 1.2 million elements
time step: 0.01 sn
iteration: 8

And the problem is that: Tke and water residuals don't convergence. momentums and continuity is 10^-3 or 10^-4

If there is any one to help me, I am so glad...

rock_bottom · October 1, 2013, 14:50

Might be a problem with the BC you apply!!

sdkozm · October 3, 2013, 04:10

sorry could you explain what is BC?

Is it boundary condition?

If it is,

Sides is symmetry plane,
Top is slip Wall
floor is velocity inlet
presure outlet
and velocity inlet
finally all hull components are Wall

Sideshore · October 8, 2013, 08:40

Hi,

First of all, the residuals in Star-CCM+ are made non-dimensional with respect to the start of the simulation. Therefore it can be hard to check convergence by using the residuals, especially for multiphase flows, often it is more convenient to look at the forces (the resistance for example).

Your BC seems alright. I normally use:

Velocity inlet for:
Inlet, Bottom, Top, Sides

Pressure outlet for:
Outlet

If the figure you are showing is the complete domain, you might want to increase the length behind the vessel and give the waves more time to damp. You can either damp the waves by increasing your cell size or by using the VOF damping option (see the manual).

Good luck!

sdkozm · October 8, 2013, 12:00

First of all thank you for your reply. The forces converge.

But,

When I use velocity inlet BC for sides after about 5000 iterations later sdr value increase more and more.

What does it mean? Besides if you want I can send you my simulation file, I hope, I don't disturb you.

Thank you again...

September 30, 2013, 06:13	Hull resistance analysis Residual problem	#1
sdkozm New Member Sdk Join Date: Sep 2013 Posts: 3 Rep Power: 12	Hi friends... I have a problem with my simulation. I try to calculate hull resistance, and the brief information about my simulation is that: about 1.2 million elements time step: 0.01 sn iteration: 8 And the problem is that: Tke and water residuals don't convergence. momentums and continuity is 10^-3 or 10^-4 If there is any one to help me, I am so glad...

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October 1, 2013, 14:50		#2
rock_bottom New Member Join Date: Jun 2013 Posts: 2 Rep Power: 0	Might be a problem with the BC you apply!!

October 8, 2013, 08:40		#4
Sideshore New Member Jan Willem Krijger Join Date: May 2010 Posts: 8 Rep Power: 15	Hi, First of all, the residuals in Star-CCM+ are made non-dimensional with respect to the start of the simulation. Therefore it can be hard to check convergence by using the residuals, especially for multiphase flows, often it is more convenient to look at the forces (the resistance for example). Your BC seems alright. I normally use: Velocity inlet for: Inlet, Bottom, Top, Sides Pressure outlet for: Outlet If the figure you are showing is the complete domain, you might want to increase the length behind the vessel and give the waves more time to damp. You can either damp the waves by increasing your cell size or by using the VOF damping option (see the manual). Good luck!

October 8, 2013, 12:00		#5
sdkozm New Member Sdk Join Date: Sep 2013 Posts: 3 Rep Power: 12	First of all thank you for your reply. The forces converge. But, When I use velocity inlet BC for sides after about 5000 iterations later sdr value increase more and more. What does it mean? Besides if you want I can send you my simulation file, I hope, I don't disturb you. Thank you again...